1. Field of the Invention
The present invention relates to a toner image fixing method for fixing toner images to a support for use in an electrophotographic image formation apparatus for forming images with toner, such as copying machines, facsimile apparatus and printers. The present invention also relates to an image fixing apparatus using the toner image fixing method.
2. Discussion of Background
In recent years, the demand for rational use of natural resources and energy is increasing for the protection of the global environment. With respect to the electrophotographic image formation apparatus, the development of the technology has tended to be directed to the reduction of power consumption for the rational use of energy, in particular, in the field of image fixing technology. This is because considerable power is consumed in image fixing. Thus, advances have been made in the technology of low-temperature image fixing.
In order to realize the low-temperature image fixing, as a matter of course, the softening point or melting point of the toner has to be lowered. When the softening point or melting point of a thermoplastic resin used in the toner is lowered, the melt viscosity of the resin is inevitably lowered since this is the nature of the thermoplastic resin. The softening point or the melting point of the thermoplastic resin depends upon, for instance, the molecular weight, the molecular weight distribution, the degree of crystallinity, the degree of cross-linking, and the intermolecular force of the resin.
In order to lower the softening point or the melting of a resin with the same structure, the degree of cross-linking has to be lowered or the molecular weight distribution has to be made narrower. There is a lower limit to the molecular weight distribution due to the limit of the preservability of the resin, so that the molecular weight has to be lowered. When the molecular weight is lowered, the molecular weight distribution is narrowed as an inevitable consequence.
Generally, when the molecular weight is lowered, the molecular chains are shortened, so that the tangling of the molecular chains becomes loose. The result is that the melt viscosity of the resin is lowered. When the molecular weight distribution is narrowed, the tangling of the molecular chains also becomes loose, so that the melt viscosity of the resin is lowered. Furthermore, when the degree of intermolecular cross-linking is lowered, the molecules become easy to move individually, so that the melt viscosity of the resin is also lowered.
Even when a toner with such a lowered melt viscosity as mentioned above is used, image fixing can be carried out without causing the so-called offset phenomenon (the phenomenon that a printing medium stays on a film sheet, hereinafter simply referred to as the offset) by use of the methods as disclosed in Japanese Patent Publication 51-29825, Japanese Laid-Open Patent Application 63-118291, Japanese Laid-Open Patent Application 63-118292, and Japanese Laid-Open Patent Application 63-118293.
Japanese Patent Publication 51-29825 discloses an image fixing method comprising the steps of applying heat to a material to be fixed at an image fixing portion comprising a film sheet, cooling the film sheet and the material to be fixed while maintaining the film sheet and the material in close contact, and peeling the film sheet away from the material (toner) when the material has been solidified. In this image fixing method, the concept of forced cooling is included, and there are specifically described a blower and a water cooler for performing the forced cooling.
The image fixing methods described in Japanese Laid-Open Patent Application 63-118291, Japanese Laid-Open Patent Application 63-118292, and Japanese Laid-Open Patent Application 63-118293, have made it possible to perform image fixing on a film, without causing the offset, in a continuous on-machine state, even when a hot-melt printing medium with a low viscosity which comprises wax as the main component is used.
Generally, the printing medium for use in thermal image transfer comprises wax as the main component, and the wax has a viscosity of about 10 to 104 centipoise. Even when the printing medium with such a low viscosity is used, the offset is not caused as long as the above-mentioned methods are used.
More specifically, in the above-mentioned methods, the film sheet is peeled off when the temperature of the fused material is lowered below a top peak of the heat of fusion measured by a differential scanning calorimeter (DSC)
In particular, in Japanese Laid-Open Patent Application 63-118291, the offset is prevented from occurring by forced cooling, which is carried out by blowing air, or by use of water or an olefin gas as cooling medium.
In Japanese Laid-Open Patent Application 63-118292, a film sheet is caused to pass through a cooling section, in close contact with an image transfer material to which a toner image is to be fixed, to prevent the occurrence of the offset, whereby the occurrence of the offset is prevented.
Further, in Japanese Laid-Open Patent Application 63-118293, there is provided a mechanism for peeling the film sheet away from the image transfer material, and also there is provided a mechanism for maintaining the film sheet in close contact with the image transfer material until the film sheet is peeled away from the image transfer material, whereby the occurrence of the offset is prevented.
By these above-mentioned methods, the toner with a lower viscosity than that of conventional toners can be used without the occurrence of the offset.
The above-mentioned methods have no particular problem as long as a conventional toner with a relatively high melt viscosity of more than 1013 centipoise is used. However, when a toner with a melt viscosity of 1013 centipoise or less is used, a problem that loud noise is caused by an image fixing member and/or a toner image bearing support is vibrated. This is because when the toner with a melt viscosity of 1013 centipoise or less is used, the adhesion of the toner to a film-shaped or belt-shaped image fixing member which is trained over a roller is so strong that when image fixing is carried out with the application of heat and pressure to the toner image bearing support, the toner image bearing support sticks to the image fixing member via the toner, and when the image bearing support begins to be separated from the film-shaped or belt-shaped image fixing member, the image fixing member is pulled up to its elastic limit together with the image bearing support, and when the image bearing support is finally separated from the image fixing member, the toner image bearing support and/or the image fixing member is considerably vibrated, making loud noise.
FIG. 3 and FIG. 4 are diagrams in explanation of the above-mentioned problem which is caused when the toner image bearing support is peeled away from the image fixing member.
In FIG. 3 and FIG. 4, reference numeral 1 indicates a heat application and image fixing roller with an inner heater 2 built in. Reference numeral 3 indicates a cooling roller which is rotated together with the heat application and image fixing roller 1 by an image fixing belt 4 which is trained over the heat application and image fixing roller 1 and the cooling roller 3. Reference numerals 5 and 6 respectively indicate counter pressure applications rollers disposed in pressure contact with the heat application and image fixing roller 1 and the cooling roller 3.
With reference to FIG. 3, a sheet of paper P with a toner image made of a toner T formed on a front side thereof which is directed to the image fixing belt 4 is caused to pass between the heat application and image fixing roller 1 and the pressure application roller 5, and is then transported in contact with the image fixing belt 4 toward between the cooling roller 3 and the pressure application roller 6. The sheet of paper P, passing through the nip between the cooling roller 3 and the pressure application roller 5, is suddenly peeled off the image fixing belt 4 at a portion A shown in FIG. 3 the moment the adhesion of the toner T to the image fixing belt 4 exceeds its limit. This peeling of the sheet of paper P away from the image fixing belt 4 is repeated, whereby the sheet of paper P is vibrated, generating the noise.
With reference to FIG. 4, when the sheet of paper P has passed through the nip between the cooling roller 3 and the pressure application roller 6 in the same manner as mentioned above, the image fixing belt 4 is slackened, yielding to the bending strength of the sheet of paper P at a portion A in FIG. 4, and the sheet of paper P is peeled off the image fixing belt 4 the moment the adhesion of the toner T to the image fixing belt 4 exceeds its limit. This peeling of the sheet of paper P away from the image fixing belt 4 is repeated, whereby the sheet of paper P is vibrated, generating the noise.
These problems tend to become conspicuous as the melt viscosity of the toner is lowered.
It is therefore a first object of the present invention to provide a toner image fixing method from which the above-mentioned conventional problems, which are caused when the toner with a low melt viscosity is used, are eliminated, and which is capable of performing image fixing in a stable manner without generating adverse abnormal vibrations of the image fixing member and/or the toner image bearing support such as a toner image transfer sheet when the toner image bearing support is peeled off the image fixing member, even when a toner with a low melt viscosity is used.
A second object of the present invention is to provide a toner image fixing apparatus for carrying out the above-mentioned toner image fixing method.
The first object of the present invention can be achieved by a method of fixing a toner image on a support, comprising the steps of:
heating a toner image formed on a support by use of a toner to the softening point or melting point of the toner or above, using an image fixing member, the toner comprising 100 parts by weight of a resin and at least 0.05 parts by weight of a wax component, the toner having a melt viscosity of 10 to 1013 centipoise,
allowing the heated toner image to cool or cooling the toner image, and
peeling the support which bears the toner image thereon away from the image fixing member when the temperature of the toner image has reached a temperature below the softening point or melting point of the toner.
The second object of the present invention can be achieved by a toner image fixing apparatus for fixing a toner image on a support, the toner image being formed by use of the same toner as mentioned above, comprising:
a pair of image fixing members for transporting therebetween the support which bears the toner image thereon, and heating the toner image to the softening point or melting point of the toner or above,
a cooling member for allowing the toner image to cool or cooling the toner image to a temperature below the softening point or melting point of the toner, and
a peeling member for peeling the support which bears the toner image thereon from the image fixing members when the toner image has been cooled to a temperature below the softening point or melting point of the toner.
By use of the image fixing apparatus with the above-mentioned structure, even when the above-mentioned toner with a relatively low melt viscosity of 10 to 1013 centipoise, the wax component works as a release agent, so that the toner image bearing support can be smoothly peeled off the image fixing member, so that there can be controlled the generation of the adverse abnormal vibrations and noise when the toner image bearing support is peeled off the image fixing members.
In the above toner image fixing apparatus, it is preferable that the peeling members be capable of peeling the support away from the image fixing members in a direction with an angle of 10 degrees or more away from the direction in which the support is transported prior to the peeling of the support away from the image fixing members.
By use of the image fixing apparatus with the above-mentioned structure, the toner image bearing support can be smoothly peeled off the image fixing members.
In the above toner image fixing apparatus, at least one of the image fixing members is in the shape of a roller, or in the shape of a belt. When the image fixing member is in the shape of a belt, the belt-shaped image fixing member may be a film- or sheet-shaped belt.
Furthermore, in the above toner image fixing apparatus, at least one of the image fixing members may be an image fixing roller which is capable of applying heat to the toner image to the softening point or melting point of the toner or above, and the cooling member may be a cooling roller, and the toner image fixing apparatus further comprising:
a transportation belt which is trained over the image fixing roller and transports the support which bears the toner image thereon onto the image fixing roller, from which transportation belt the support can be moved away after the support passes over the image fixing roller.
In the image fixing apparatus with the above-mentioned structure, the support, after being heated by the image fixing roller, is no longer heated or receives no restrictions, so that the cooling of the support can be carried out quickly, and therefore the support can be smoothly peeled away from the image fixing member.
Furthermore, in the above toner image fixing apparatus, at least one of the image fixing members may be an image fixing roller which is capable of applying heat to the support which bears the toner image thereon to the softening point or melting point of the toner or above, and the cooling member may be built in the image fixing roller, which is actuated so as to cool the toner image after the application of heat to the toner image by the image fixing roller is terminated.
By use of the image fixing apparatus with the above-mentioned structure, after the toner image bearing support is heated by the image fixing roller, the heat from the image fixing roller can be efficiently cancelled by the cooling roller, so that the cooling of the toner image can be quickly carried out, and accordingly, the support can be smoothly peeled away from the image fixing member.